Process and electrolyte effects on the nitrogen-doped anodic plasma electrolytic saturation coating electrochemical performance: Simultaneous participation of the applied and breakdown voltages

Abstract

Anodic plasma electrolytic saturation (APES) is an eco-friendly method to deposit a composite coating for improving the performance of metal substrates. This study had investigated the corrosion behaviour of the nitrogen-doped Al2O3 layers deposited in alkaline-nitrite electrolytes at constant VAPES of 500 and 450 V. The results indicated that the coatings prepared at a lower VAPES had higher macro and microscopic qualities and electrochemical resistance than the higher VAPES. At the VAPES = 500 V, the best APES coating just had electrochemical resistance with 1.030 MΩ.cm2 values after 48 h of immersion in the 3.5 wt% sodium chloride medium. Based on this study's results, the vital ∆V parameter is the coating driving force that depends on changes in the breakdown voltage (VB.D.) and applied voltage value (VAPEP). This participation dependent parameter (∆V) significantly affects the macro and micro-quality of this nitrogen-doped composite coating and its corrosion behaviour. The APES coating deposited at a lower NaNO2 amount (1 g/L) and VAPEP of 450 V had the highest spinel and cubic nitrogenous phases and more closed pores than the best layer deposited at 500 V due to removing KOH and decreasing VAPEP and consequently declining the participation dependent parameter (∆V) value. Accordingly, this nitrogen-doped APEP coating with the best chemical-physical properties experienced the remarkably highest electrochemical resistance with the 353.500 MΩ.cm2 value compared to all studied samples and uncoated aluminium substrate after 48 h immersion time.